In a crits race I could normally stay with the bunch but yesterday there was a smaller group in the race. I got dropped as there were more surges than I was used to. I check the heart rate graph after the race, I was very much in the red a few times. 188 hr (max 196). How do you train for this? Interval work?
Interval work to get ready for the surges for sure. I'd also recommend adding some tempo riding. For me, that helped a lot in priming the aerobic engine. Your goal should be to raise you aerobic ability so that you aren't forced to go into your red zone that often.
Depends upon what went first when you got dropped, your aerobic system or your legs? Looks like in this case, it was your heart&lungs. How did your legs feel at the time? If they felt fine, then use bigger gears next time. This will stress the legs more and the aerobic-system less. This is where having a straight-block cluster comes in handy as you can adjust leg-effort in 5-rpm increments.
Training with short intervals & sprints will work on the legs. Longer intervals, tempos and long hillclimbs will help with the cardio system.